1. Field of the Invention
The present invention relates to a useful vacuum pump, for experimental or industrial vacuum apparatuses, such as particle accelerators, experimental and research apparatuses for nuclear fusion or isotope separation, electron microscopes, and analyzing and measuring apparatuses such as surface analyzers, and semiconductor manufacturing systems capable of surely creating a clean vacuum under intake pressure conditions ranging from atmospheric pressure through a high vacuum to a ultra-high vacuum.
2. Discussion of the Background
Shown in FIG. 50 is an exemplary conventional vacuum pump comprising a casing a, a rotor shaft c journaled on the casing a, and a rotor disk b fixedly mounted on the rotor shaft c within the casing a. Spiral grooves d are formed respectively in the opposite inner surfaces of the casing a. The outer ends of the spiral grooves d connect with an inlet port e, and the inner ends of the spiral grooves d connect respectively with outlet port f. When the rotor disk b is rotated, gas sucked through the inlet port e is compressed between the spiral grooves d and the rotor disk b, and then the compressed gas is discharged through the outlet ports f.
To provide the conventional vacuum pump with a high compressive performance, the spiral grooves d must be formed of a sufficiently large length, and hence the spiral grooves d cannot be formed with a large width. When the depth of the spiral grooves d is large relative to the width of the same, the pumping performance of the vacuum pump is deteriorated. Accordingly, it is impossible to form the spiral grooves over a large sectional area. When a plurality of these vacuum pumps are combined in a multi-stage construction to provide a multi-stage vacuum pump having a high compression ratio, connecting passages of a complicated construction must be formed between the adjacent rotor chambers of the vacuum pump when spiral grooves are formed in the opposite inner surfaces of each rotor chamber. When parallel action of both sides of the rotor disk is impossible, it is difficult to provide the vacuum pump with a high pumping speed. When the sectional area of the spiral grooves d is increased to provide a vacuum pump having a high pumping speed, the diameter of the rotor disk b must be increased accordingly, and hence the size of the vacuum pump is increased.